Each type has its own strengths and weaknesses, most of which are logical setups. Fire-type Pokémon are weak to Water-type Pokémon, Ice-type Pokémon are weak to Fire-type Pokémon, Water-type Pokémon are weak to Electric-type Pokémon, etc. These matchups also apply to the types of moves as well: A Fire-type move such as Ember will be strong against a Grass-type Pokémon such as Bulbasaur. Some types of Pokémon are also immune to a certain type of moves, regardless of its attack power, such as using an offensive Ghost-type move on a Normal-type Pokémon.

Pokémon themselves can have up to two types, making them Dual-Type Pokémon, but moves can only be one type (with the exception of the move Flying Press which is a Fighting/Flying-type move). Most if not all dual-type Pokémon's types correspond with one another such as a Grass/Poison-type Pokémon such as Bulbasaur, or a Rock/Ground-type Pokémon such as Onix. However, not all dual-type Pokémon's types relate to each other like this. Some Pokémon may be dual-type between two types that don't normally go together such as Water/Electric-types (such as Lanturn) or Grass/Water types (such as Ludicolo) or Grass/Flying-types (such as Jumpluff), or Fighting/Psychic (such as Medicham). Some dual-type Pokémon lose one of their types and gain a different type upon Evolution such as Scyther (a Bug/Flying-type) which evolves into Scizor (a Bug/Steel-type). Some singular type Pokémon will change completely to a different type or types upon evolution, such as Azurill (a Normal/Fairy-Type) which evolves into Marill (a Water/Fairy-Type) or Eevee (a Normal-Type) which can evolve into Flareon (a Fire-Type), Jolteon (an Electric-Type), Vaporeon (a Water-Type), Espeon (a Psychic-Type), Umbreon (a Dark-Type), Glaceon (an Ice-Type), Leafeon (a Grass-Type) or Sylveon (a Fairy-Type).

Unused Typings

There are currently 38 unused dual types in pokemon (gen 7 pokemon types are in this list)

Trivia

Due to this, several Pokémon have been retyped to take advantage of the addition of new types, with the entire Magnemite line retyped to Electric/Steel and many others becoming Fairy-type following its introduction.